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United States Patent |
5,774,216
|
Priddy
,   et al.
|
June 30, 1998
|
RLG dither noise injection by means of reference modulation
Abstract
To reduce the accumulative lock-in effects of the ring laser gyroscope, the
dither circuitry is provided with low frequency dither amplitude
modulation. Such modulation is achieved by first developing a pair of
complementary low frequency dither noise signals. These low frequency
dither noise signals are then utilized by a modulator to modulate the
dither drive signal in conjunction with the low frequency dither noise
signals. This results in a system which allows much more dither amplitude
modulation with much less output from the drive amplifiers. Because of the
ability to increase amplitude modulation, gyro performance is greatly
improved.
Inventors:
|
Priddy; Lloyd W. (Mohtomedi, MN);
Sewell; Wesley C. (Dunedin, FL)
|
Assignee:
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Honeywell, Inc. (Minneapolis, MN)
|
Appl. No.:
|
160003 |
Filed:
|
November 30, 1993 |
Current U.S. Class: |
356/475 |
Intern'l Class: |
G01C 019/70 |
Field of Search: |
356/350
|
References Cited
U.S. Patent Documents
3467472 | Sep., 1969 | Killpatrick | 356/350.
|
4445779 | May., 1984 | Johnson | 356/350.
|
4551021 | Nov., 1985 | Callaghan et al. | 356/350.
|
4592656 | Jun., 1986 | Egli | 356/350.
|
4606637 | Aug., 1986 | Green | 356/350.
|
4653920 | Mar., 1987 | Green | 356/350.
|
4657392 | Apr., 1987 | Egli | 356/350.
|
4695160 | Sep., 1987 | Egli | 356/350.
|
4839650 | Jun., 1989 | Green et al. | 341/118.
|
Primary Examiner: McGraw; Vincent P.
Attorney, Agent or Firm: Lervick; Craig J.
Claims
What is claimed is:
1. A dither drive for driving a dither apparatus so as to rotationally bias
a ring laser gyroscope, the dither drive comprising:
pick-off means for producing a pick-off signal indicative of the rotational
motion of the dither apparatus;
pick-off amplifying means for receiving the pick-off signal and amplifying
the pick-off signal to produce an amplified pick-off signal;
squaring circuit means for receiving the amplified pick-off signal and
producing a square wave signal having a frequency equal to that of the
amplified pick-off signal;
a noise source for generating a random noise signal;
modulating means for receiving the random noise signal and the square wave
signal, the modulating means for generating an amplitude modulated signal
in response to the square wave signal and the random noise signal wherein
the amplitude modulated signal has a frequency equivalent to that of the
square wave signal; and
summing means for receiving the amplitude modulated signal, the square wave
signal, and the amplified pick-off signal, and producing a dither drive
signal which is equal to the sum of the amplitude modulated signal, the
square wave signal, and the amplified pick-off signal.
2. The dither drive of claim 1 wherein the noise source generates the
random noise signal with all frequency components below a predetermined
level.
3. The dither drive of claim 1 wherein the squaring circuit is an
operational amplifier having a negative feedback configuration, wherein
the negative feedback configuration consists of a first zener diode and a
second zener diode connected in series with one another, the series
combination connected between the amplifier output and the amplifier
negative input.
4. The dither drive of claim I further comprising an inverting means
connected to the noise source so as to receive the random noise signal and
produce an inverted random noise signal, the inverted random noise signal
and the random noise signal creating a pair of complementary noise
signals.
5. The dither drive of claim 1 wherein the modulating means has a first
relay and a second relay, the first relay having an input connected to the
random noise signal, the second relay having an input connected to the
inverted random noise signal, the first relay and the second relay having
an inversely coupled relay drive for switching the first relay and the
second relay, the coupled relay drive connected to an output of the
squaring circuit means, the first relay and the second relay further
having a coupled output for producing the amplitude modulated signal.
6. The dither drive of claim 4 wherein the squaring circuit means and the
modulating means are comprised of an amplifier having a negative feedback
network attached between an output of the amplifier and a negative input
of the amplifier, the negative feedback network being attached to the
noise source and the inverting means so as to receive the pair of
complementary noise signals.
7. The dither drive of claim 6 wherein the negative feedback network causes
the effective amount of negative feedback to be altered so as to
correspond with the complementary noise signals.
8. The dither drive of claim 6 wherein the negative feedback network
comprises a series connection of a first resistor and a second resistor
attached between the inverting means and a negative voltage supply, a
third resistor is attached between the amplifier output and a first common
node connecting the first resistor and the second resistor, attached
between the first common node and the amplifier negative input is a first
diode, the negative feedback network further comprising a series
connection of a fourth resistor and a fifth resistor connected between the
noise source and a positive voltage supply, a sixth resistor is attached
between the amplifier output and a second common node between the fourth
resistor and the fifth resistor, and attached between the second common
node and the amplifier negative input is a second diode.
9. The dither drive of claim 2 wherein the predetermined level is 20 hertz.
10. A biasing system for a ring laser gyroscope for providing a rotational
bias so as to eliminate the effects of lock in, the ring laser gyroscope
having a block for supporting two counterpropagating optical signals, the
biasing system comprising:
a dither means for rotating the ring laser gyroscope block;
a dither pick-off for sensing the rotation of the ring laser gyroscope
block and producing a pick-off signal at a pick-off output;
a squaring means having an input attached to the pick-off output, the
squaring means for producing a squared-up signal at a squaring means
output, the squared-up signal being a square wave having a frequency and
phase related to the pick-off signal;
a low frequency noise source for producing a random noise signal at a noise
source output;
inverting means having an input connected to the noise source output for
receiving the low frequency noise signal, the inverting means for
producing an inverted noise signal on an inverting means output, the
inverted noise signal being of equal magnitude and opposite polarity from
that of the random noise signal;
modulating means having a first input connected to the noise source output,
a second input connected to the inverting means output, and a third input
connected to the squaring means output, the modulating means for producing
an amplitude modulated square wave at a modulating means output, the
amplitude modulated square wave having its frequency and phase related to
that of the squared-up signal and having its amplitude related to the
random noise signal; and
summing means having a first input attached to the modulating means output,
a second input attached to the pick-off output, and a third input attached
to the squaring means output, the summing means having an output for
producing a dither drive signal equivalent to the sum of the signals
present at the first input, the second input, and the third input, the
summing means output attached to the dither means for controlling the
rotational motion of the dither motor.
11. The biasing system of claim 10 wherein the random noise signal has all
its frequency components below a predetermined level.
12. The biasing system of claim 11 wherein the predetermined level is 20
hertz.
13. The biasing system of claim 10 wherein the dither pick-off further
comprises a pick-off sensor and an amplifying means, the pick-off sensor
being attached to the dither means for detecting the motion of the dither
means and producing a sensor signal, the amplifying means attached to the
pick-off sensor for receiving the sensor signal and producing the pick-off
signal, the pick-off signal being an amplification of the sensor signal.
14. The biasing system of claim 10 wherein the squaring means comprises an
amplifier having connected between an amplifier output and an amplifier
negative input, a parallel connected resistor and double anode zener
diode.
15. The biasing system of claim 10 wherein the low frequency noise source
includes a low pass filter for receiving a broad range noise signal and
filtering to produce the low frequency noise signal.
16. The biasing system of claim 10 wherein the modulating means has a first
relay and a second relay, the first relay having an input connected to the
random noise signal, the second relay having an input connected to the
inverted random noise signal, the first relay and the second relay having
an inversely coupled relay drive for switching the first relay and the
second relay, the coupled relay drive connected to an output of the
squaring circuit means, the first relay and the second relay further
having a coupled output for producing the amplitude modulated signal.
17. The biasing system of claim 10 wherein the squaring means and the
modulating means are comprised of an amplifier having a negative feedback
network attached between an output of the amplifier and a negative input
of the amplifier, the negative feedback network being attached to the
noise source and the inverting means so as to receive the pair of
complementary noise signals.
18. The biasing system of claim 17 wherein the negative feedback network
causes the effective amount of negative feedback to be altered so as to
correspond with the complementary noise signals.
19. The biasing system of claim 17 wherein the negative feedback network
comprises a series connection of a first resistor and a second resistor
attached between the inverting means and a negative voltage supply, a
third resistor is attached between the amplifier output and a first common
node connecting the first resistor and the second resistor, attached
between the first common node and the amplifier negative input is a first
diode, the negative feedback network further comprising a series
connection of a fourth resistor and a fifth resistor connected between the
noise source and a positive voltage supply, a sixth resistor is attached
between the amplifier output and a second common node between the fourth
resistor and the fifth resistor, and attached between the second common
node and the amplifier negative input is a second diode.
20. A method for rotationally biasing a ring laser gyroscope so as to
reduce the effects of lock-in, the method comprising the steps of:
(a) monitoring a dither pick-off, the dither pick-off situated so as to
detect a motion of the ring laser gyroscope and produce a pick-off signal
indicative of such motion;
(b) generating a pair of complementary noise signals, the complementary
noise signals having all of their frequency components below a
predetermined level, the complementary noise signals being of equal
magnitude and phase, but opposite polarity;
(c) generating a squared-up signal by receiving the pick-off signal and
producing a square wave signal having a frequency and phase equal to that
of the pick-off signal;
(d) generating an amplitude modulated signal by receiving the complementary
noise signals and the squared-up signal and generating the amplitude
modulated signal such that the amplitude modulated signal has the
frequency and phase of the squared-up signal and the amplitude of the
complementary noise signals; and
(e) summing the amplitude modulated signal, the squared-up signal, and the
pick-off signal to produce a dither drive signal, the dither drive signal
being an amplitude modulated signal that can be used to rotationally bias
the ring laser gyroscope.
21. The method of claim 20 wherein the predetermined level is 20 hertz.
22. A dither drive apparatus having random noise injection for dithering a
ring laser gyroscope, the dither drive apparatus comprising:
a low frequency random noise generator for generating a first noise signal
and a second noise signal both of which have all their frequency
components below a predetermined level, the first noise signal and the
second noise signal being complementary having equal frequency and phase
but opposite polarity, the first noise signal being produced at a first
output and the second noise signal being produced at a second output;
dither pick-off means for sensing the dither induced motion of the ring
laser gyroscope, the dither pick-off having an output for producing a
dither pick-off signal;
modulating means having a first input attached to the noise generator first
output, a second input attached to the noise generator second output, and
a third input attached to the dither pick-off output, the modulating means
for producing an amplitude modulated square wave signal having a frequency
equal to that of the dither pick-off signal while having a random
amplitude, said random amplitude controlled by the first noise signal and
the second noise signal, the amplitude modulated square wave signal being
produced at a modulating means output; and
summing means attached to the modulating means output and the dither
pick-off output, the summing means for producing a dither drive signal
equal to the sum of the amplitude modulated square wave signal and the
dither pick-off signal.
23. The dither drive apparatus of claim 22 wherein the predetermined level
is 20 hertz.
24. The dither drive apparatus of claim 22 wherein the dither pick-off
further comprises a pick-off sensor and an amplifying means, the pick-off
sensor being attached to the dither means for detecting the motion of the
dither means and producing a sensor signal, the amplifying means attached
to the pick-off sensor for receiving the sensor signal and producing the
pick-off signal, the pick-off signal being an amplification of the sensor
signal.
25. The dither drive apparatus of claim 22 wherein the low frequency noise
generator further comprises:
a low pass filter for receiving a broad range noise signal and filtering to
produce the first low frequency noise signal; and
an inverter for receiving the first low frequency noise signal an inverting
it to produce the second low frequency noise signal.
26. The dither drive apparatus of claim 22 the modulating means is
comprised of an amplifier having a negative feedback network attached
between an output of the amplifier and a negative input of the amplifier,
the negative feedback network being attached to the low frequency noise
generator.
27. The dither drive apparatus of claim 26 wherein the negative feedback
network causes the effective amount of negative feedback to be altered so
as to correspond with the complementary noise signals.
28. The biasing system of claim 26 wherein the negative feedback network
comprises a series connection of a first resistor and a second resistor
attached between the inverting means and a negative voltage supply, a
third resistor is attached between the amplifier output and a first common
node connecting the first resistor and the second resistor, attached
between the first common node and the amplifier negative input is a first
diode, the negative feedback network further comprising a series
connection of a fourth resistor and a fifth resistor connected between the
noise source and a positive voltage supply, a sixth resistor is attached
between the amplifier output and a second common node between the fourth
resistor and the fifth resistor, and attached between the second common
node and the amplifier negative input is a second diode.
Description
FIELD OF THE INVENTION
The present invention relates to a device to reduce the lock-in effects of
a ring laser gyroscope. More specifically, the present invention provides
a device for injecting low frequency, random noise into a dither biasing
system.
BACKGROUND OF THE INVENTION
As is well known in the art, a ring laser gyroscope utilizes two
counterpropagating electromagnetic waves, or beams of light, to detect
inertial rotation. In summary, the two light beams are caused to propagate
in opposite directions around a closed-loop path. Rotation of this
closed-loop path causes the effective pathlength in one direction to
become shorter while lengthening the effective pathlength in the other
direction. This change in optical pathlength is a direct measure of
inertial rotation. Further, details regarding the general operation of a
ring laser gyroscope may be found by referring to U.S. Pat. No. 3,373,650,
by J. E. Killpatrick, entitled "Ring Laser Angular Rate Sensor," U.S. Pat.
No. 3,467,472, by J. E. Killpatrick, entitled "Random Bias for Angular
Rate Sensor," or U.S. Pat. No. 4,152,071, by Theodore J. Podgorski,
entitled "Control Apparatus," all of which are assigned to Assignee of the
present invention.
As disclosed in U.S. Pat. No. 3,373,650 to Killpatrick, when the ring laser
gyroscope sits at rest, or is subjected to low input rates, the two
counterpropagating light beams tend to resonate together or "lock-in".
This tendency to lock-in reduces the gyroscope's ability to measure
rotation at low rates. To alleviate the problem of lock-in it was
suggested in U.S. Pat. No. 3,373,650 that the ring laser gyroscope be
subjected to a bias. This bias was in the form of a dithering signal
wherein the ring laser gyroscope is rotationally oscillated, resulting in
the gyroscope seeing an input rate for substantial periods of time. It was
recognized that if this bias was periodic, then the output signal could be
integrated over the bias period and any output due to the bias signal over
this integration period would be zero. Therefore, any output over the
integrated time period would be due to inertial rotation rather than the
biasing.
It was further recognized in U.S. Pat. No. 3,467,472 that while the
gyroscope is subjected to a periodic bias, there are still periods of time
at which the gyroscope is subjected to zero input. These time periods
occur at the bias turnarounds, or dither turnarounds, where the gyroscope
dither stops to reverse its direction. It was suggested that these periods
of zero input resulted in a cumulative lock-in error which resulted in a
cumulative error in the gyro's output. This a cumulative error is further
known as Angular Random Walk (ARW). As a means to alleviate the problems
of a cumulative lock-in errors, a random bias signal was introduced to the
dither biasing means. As taught in U.S. Pat. No. 3,467,472, a random noise
signal was summed into the dither drive signal generator, thus resulting
in a randomized dither drive signal. This random noise signal has the
effective of randomizing the cumulative lock-in error, thus greatly
reducing the long term effects of lock-in.
U.S. Pat. No. 4,695,160 to Egli, which is assigned to the Assignee of the
present invention, further taught that the amplitude of the periodic bias
can be altered to also aid in the reduction of a cumulative lock-in error.
This patent suggests that this amplitude alteration can be achieved by the
addition of a high frequency, random noise signal to the dither drive.
Another example of a method to reduce the lock-in phenomena is U.S. Pat.
No. 4,653,920 to Geen. This patent describes a dither system using a so
called pseudo-random sequence generator to produce random noise. The so
called pseudo-random sequence generator is based on a shift-register.
While this solution provides one way of providing random noise to the
dither motor, the problem of amplifier saturation must be dealt with
because high frequency noise is added to the dither drive. As a result of
amplifier saturation, the amount of amplitude variation is limited by the
saturation point of the amplifiers.
In U.S. Pat. No. 4,445,779 to Johnson drive circuits are sampled by an A to
D converter and then signal processing is used to generate a dither drive
signal. During the signal processing random noise is summed with the
dither drive to force successive dither peaks into a random pattern. The
dither modulation described is limited by the drive power available and by
the maximum voltage which can be applied to the piezoelectric motor.
Therefore, the amount of actual modulation obtainable is somewhat limited.
In summary, all of the prior art approaches to eliminate the effects of
lock-in by providing the dither signal with a random noise component have
utilized the approach of summing in high frequency random noise. When this
high frequency random noise is summed with the dither drive output signal,
the amount of noise obtainable is severely limited by the saturation point
of the amplifiers. Other approaches have used complex signal processing
which requires additional circuitry such as digital signal processors or
microprocessors. Even when signal processing is utilized to inject a high
frequency noise signal, the amount of modulation is, again, severely
limited by the output stage of the amplifier.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a means of noise
modulation for the dither drive circuitry of a ring laser gyroscope. It is
a further object of the present invention to provide a dither drive
modulation system that will not require a dramatic increase in the voltage
necessary to operate the system.
It is another object of the present invention to provide a low frequency
dither modulation technique which will reduce the effects of low rate
lock-up, or lock-in, in a ring laser gyroscope while not requiring an
increase in the power necessary to drive the dither system.
In one embodiment of the invention, low frequency dither modulation is
achieved by first filtering low frequency noise through a low pass filter.
The output of this low pass filter is then fed into an inverter such that
the output from the filter and the output from the inverter form
complementary low frequency, noise signals. These complementary signals
are then fed into a modulator.
Concurrently, with the development of the complementary low frequency,
noise signals the dither pick-off signal is received from the dither motor
and is fed into a pick-off amplifier. The output from this pick-off
amplifier is fed into a squaring circuit which creates a square wave in
phase with the dither pick-off signal. The squaring circuit output is then
fed into the modulator in conjunction with the complementary noise signals
to create an amplitude modulated square wave signal. The modulation is
directly controlled by the low frequency noise signal. This amplitude
modulated square wave signal is then fed into a summing circuit. Also,
input to the summing circuit is the output from the pick-off amplifier
which results in the summing circuit output being an amplitude modulated
dither drive signal. The amplitude modulated dither drive signal is then
fed to a drive amplifier which drives the dither motor.
BRIEF DESCRIPTION OF THE DRAWINGS
Further objects and advantages of the present invention can be seen by
referring to the following detailed description in conjunction with the
drawings in which:
FIG. 1 is a block diagram of the dither drive system which incorporates low
frequency noise modulation;
FIG. 2 is one embodiment of the dither drive generation circuitry which
receives a low frequency noise signal and generates an amplitude modulated
dither drive signal; and
FIG. 3 is a second embodiment of a dither drive system which, again,
receives a low frequency noise signal and creates an amplitude modulated
dither drive signal at its output.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, there is shown a block diagram of a dither drive
system 10. As will be seen in the following discussion, dither drive
system 10 is a closedloop control system for driving a dither motor 20. As
is well known in the art, dither motor 20 causes rotational oscillation of
a ring laser gyroscope (not shown). Dither motor 20 has a pick-off 22
which provides a dither pick-off signal. This dither pick-off signal from
dither pick-off 22 is transmitted to a pick-off amplifier 24 which
amplifies the pick-off signal and produces a pick-off amplifier output
signal on a pick-off amplifier output 26. Typically, the signal produced
at pick-off amplifier output 26 is a pseudo-sine wave signal which is
indicative of the motion of dither motor 20. Connected to the dither
pick-off amplifier output 26 is a squaring circuit 30. Squaring circuit 30
receives the dither pick-off output signal and creates a square wave
having a frequency and phase equal to that of the signal present at
pick-off amplifier output. This square wave, or squared-up, dither signal
is then transmitted from squaring circuit 30 to a modulator 34.
Input to dither drive system 10 is a noise signal 38. This noise signal 38
is provided as an input to a low pass filter network 40. Low pass filter
network 40 has a pair of complementary outputs 42 and 44 for outputting a
low frequency noise signal on a first output 42 and outputting a second
low frequency noise signal on a second output 44. The two signals output
from low pass frequency network 40 are in phase with one another; however,
have opposite polarity. Therefore, these two signals constitute a pair of
complementary low frequency noise signals. The first filter network output
42 and second filter network output 44 are connected to modulator 34.
These two signals, as well as the signal from squaring circuit 30, are
used by modulator 34 to create an amplitude modulated square wave which is
transmitted from modulator 34 on a modulator output 36.
Modulator output 36 is connected to a summing circuit 50 as is pick-off
amplifier output 26. Summing circuit 50 sums the two input signals and
produces a dither drive signal at summing circuit output 52. The dither
drive signal produced on summing circuit output 52 is then transmitted to
a drive amplifier 60 which is used to amplify the dither drive signal and
transmit a signal on dither drive output 62 to dither motor 20. Dither
motor 20 is then driven by an amplitude modulated drive signal; the
amplitude modulation being the result of the low frequency noise signal 38
which is input to the dither drive system 10.
Referring now to FIG. 2, there is shown in more detail the circuitry
necessary to obtain the low frequency dither modulation for dither drive
system 10. As shown in FIG. 1, a noise signal 38 is input to low pass
filter network 40. Low pass filter network 40 consists of a low pass
filter 70 and an inverter 72. Noise signal 38 is input to low pass filter
70. Low pass filter 70 has an output 74 which provides a low frequency
noise signal. In the preferred embodiment, the cut-off for the low pass
filter is approximately 10-20 Hz; however, this cut-off level could be
tailored to a particular application. Filter output is then connected to
inverter 72 which inverts the signal and produces a second low frequency
noise signal at an inverter output 76. As can be seen from FIG. 2, filter
output 74 and inverter output 76 are complementary low frequency noise
signals. These are then connected to first filter network output 42 and
second filter network output 44, respectively.
First filter network output 42 and second filter network output 44 are
connected to modulator 34. In the embodiment shown in FIG. 2, modulator 34
consists of a pair of inversely coupled relays 80 and 82. First filter
network output 42 is connected to a second relay input 82 and second
filter network output 44 is connected to a first relay input 80. First
relay 78 and second relay 79 are then switched to produce an amplitude
modulated output 86.
As was discussed in reference to FIG. 1, a dither pick-off signal is
provided to a dither pick-off amplifier 24. Dither pick-off amplifier 24
then amplifies the pickoff signal and produces an amplified pick-off
signal at pick-off amplifier 26. This pick-off amplifier output 26 is then
connected to squaring circuit 30 which produces a squared-up signal, or
square wave, having a frequency and phase equal to that of the pick-off
signal.
The squaring circuit 30 comprises an amplifier 28 connected in a negative
feedback configuration. Connected between amplifier output 32 and
amplifier negative input 33 is a resistor 29. Connected in parallel with
resistor 29 is a first zener diode 46 and a second zener diode 48. First
zener diode 46 and second zener diode 48 are connected together as a
double-anode zener. The output of squaring circuit 30 is then connected to
modulator 34 and, more specifically, connected to the relay drive coils 88
which drives first relay 78 and second relay 79. Due to this connection
from squaring circuit output to relay drive 88, first relay 78 and 79 are
switched at a frequency equal to that of the squaring circuit output which
is equal to the frequency of the dither pick-off signal. Furthermore,
first relay 78 and second relay 79 are configured to be out of phase with
one another. This causes only one relay to be closed at any time.
Therefore, at amplitude modulator output 86 there is an amplitude
modulated square wave having a frequency equal to that of the dither
pick-off signal and an amplitude equal to the level of the complementary
low frequency noise signals. Modulator output 86 is then connected to
summing amplifier 50 along with pick-off amplifier 26 and squaring circuit
output 32. These signals are then summed resulting in a dither drive
signal being produced at summing circuit output 52 which has a modulated
amplitude. The modulation of the dither drive signal is in response to the
low frequency noise which is input to the circuit by noise signal 38.
Now referring to FIG. 3 wherein an alternative embodiment of the circuitry
of dither drive system 10 is shown. For clarity, like elements have
retained like reference numerals. Again, a noise signal 38 is input to a
low pass filter network 40. As was shown in FIG. 2, filter network 40
consists of a low pass filter 70 and an inverter 72. Low pass filter
network 40 produces complementary low frequency noise signals on first
filter network output 42 and second filter network output 44.
First filter network output 42 and second filter network output 44 are both
attached to a feedback network 100. Feedback network 100 is connected
across an amplifier 102 in a negative feedback configuration. Amplifier
102, in conjunction with feedback network 100, operates as a squaring
circuit as well as a modulator to provide both the squaring and modulation
functions in dither drive system 10.
Again, dither pick-off 22 is attached to pick-off amplifier 24 which has
pickoff amplifier output 26 for supplying an amplified pick-off signal.
Pick-off amplifier output 26 is resistively attached to the negative input
of amplifier 102. Also attached to the negative input of amplifier 102 is
one leg of feedback network 100.
Feedback network 100 has first network filter output 42 attached to a first
resistor 104. Attached to the opposite side of first resistor 104 is a
second resistor 106. Second resistor 106 has its other terminal attached
to a positive voltage supply. Attached to the common node between first
resistor 104 and second resistor 106 is a third resistor 108. Third
resistor 108 has its other terminal attached to the output 110 of
amplifier 102. Also attached to the common node between first resistor 104
and second resistor 106 is first diode 112. First diode 112 is connected
to have its cathode attached to the common node between first resistor 104
and second resistor 106 while its anode is connected to a negative input
114 of amplifier 102. Feedback network 100 further has second filter
network output 44 attached to a fourth resistor 116. The other terminal of
fourth resistor 116 is connected to a fifth resistor 118. Fifth resistor
118 has its second terminal connected to a negative voltage supply.
Connected to the common node between fourth resistor 116 and fifth
resistor 118 is a sixth resistor 120. Sixth resistor 120 has its second
terminal connected to amplifier output 110. Also connected to the node
between fourth resistor 116 and fifth resistor 118 is a second diode 122.
Second diode 122 is connected such that its anode is connected to the
common node between fourth resistor 116 and fifth resistor 118 whereas the
cathode is connected to amplifier negative input 114. Amplifier 102
further has a positive input which is connected to a neutral reference or
ground 124.
In operation, amplifier 102, in conjunction with feedback network 100,
functions as both a squaring circuit and a modulator to produce modulator
output 36. As will be recognized by those skilled in the art, the
connection of first filter network output 42 and second filter network
output 44 to feedback network 100 causes the feedback reference of
amplifier 102 to be altered. This results in modulator output 36 being an
amplitude modulated square wave having a frequency and phase equal to that
of pick-off amplifier output 26. Modulator output 36 is again input into
summing circuit 50 resulting in a summing circuit output 52 which is a low
frequency amplitude modulated dither drive signal.
It will be recognized by those skilled in the art that a dither drive
signal is achieved having low frequency random amplitude modulation. This
type of drive signal greatly reduces the lock-in effects of a dithered
ring laser gyroscope. Such a reduction in the lock-in effects vastly
improves the gyros performance.
In each of the embodiments of the present invention, low frequency
amplitude modulation is used in addition to summing a noise signal on the
top of the drive signal. Since this low frequency amplitude modulation is
used much more modulation can be achieved with much less drive from the
drive amplifiers. As a result of the increased modulation, the effects of
lock-in are greatly reduced and, as previously mentioned, the performance
of the gyroscope is, accordingly, increased.
Furthermore, by referring back to FIGS. 1 through 3 it will be recognized
that all of the signal manipulation is done utilizing analog circuitry.
Thus, no digital signal processors or microprocessors are necessary to
achieve the goals of the present invention.
Having described the present invention in considerable detail, it should be
apparent to those skilled in the art that certain modifications and
alterations can be made without departing from the basic ideas of the
present invention. We claim all alterations and modifications coming
within the scope and spirit of the following claims:
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